Heretofore video processing systems for quantizing, encoding and otherwise preconditioning video signals, from whatever source, prior to transfer to and manipulation by digital computers have predominantly been of the genre classifiable as "frame grabbers". The operation of a frame grabber is such that each horizontal line is scanned by, for example, a video camera or similar transducer and analytically subdivided into, typically, several hundred picture elements, the picture elements commonly referred to as "pixels". The average brightness level of each pixel is represented by an analog voltage which is in turn quantized by an analog-to-digital converter (A/D) so as to render the gray scale level, a measure of the proportional brightness of that pixel, amenable to storage and processing via a computer.
Although offering a substantial amount of quantitive information regarding the image scanned by the video camera, the frame grabbing technique suffers as an inherently slow and expensive approach to video data acquistion. The drawback is largely attributable to the requirement to process approximately 10.sup.5 pixels per frame of video information. Relatively sophisticated and commensurately expensive hardware is required to digitally encode the analog signal representing the brightness level of each pixel and thereafter transfer into memory the information so encoded. Furthermore, the technique necessitates the use of a relatively powerful, in terms of both storage as well as a computational capacity, computer in order to process the video data so acquired in anything approaching real time applications.
The video processing system contemplated by the subject invention represents a substantially simplified approach to video data acquisition and, although not generally capable of delivering quite the level of quantitive information as the frame grabber described above, has proved entirely adequate in a broad range of applications involving dimensional measurements. For example, the invention has proved quite useful in measuring the inside and outside diameters of quartz tubes in a production process.
Furthermore, the invention requires a modest amount of relatively less sophisticated circuitry in order to implement the interface of the video transducer (e.g., camera) to a computer. Furthermore, because the memory and computational demands are relaxed, it has been found possible to use relatively inexpensive microprocessors in real time measurement and control applications otherwise requiring more sophisticated computers.